One of the most exciting developments in the application of lasers to eye surgeries, the ultraviolet excimer laser is used to reshape the cornea in a procedure known as laser-in-situ-keratomileusis (LASIK).

The FDA-approved tracker, Visx Star S3 ActiveTrak™ , allows the cool beam of laser to follow numerous eye movements during the LASIK procedures. Visx study showed that 99.4% of all eye movements were accurately tracked with the tracker at 20 times per second. The Visx 3D eye tracker uses the natural pupil as a landmark to follow eye movements in the X, Y and Z directions (Three-Dimensional Eye Tracker) at 60 times per second, or 6 times per pulse of the laser. Studies have shown that the use of active eye tracking appeared to improve the optical and visual outcomes and to minimize higher-order optical errors in the eyes. The Visx Star S3 ActiveTrak™ eye tracker is directly under the control of the surgeon who will program the centration, engagement and alignment . No pharmaceutical eye drops for the dilation of the pupils are required for the tracker to work, thereby reducing the patient visual recovery time. The ActiveTrak™ system relies upon oblique infrared beams which do not interfere with the procedure.

Another important element of the new Visx technology is the Variable Spot Scanning (VSS). VSS varies the laser spot size from 0.65 to 6.5mm in diameter to permit the creation of different intricate shapes and complex configurations guided by computer algorithms. A current benefit of the VSS is a recent FDA approval to enlarge the treatment zone to 8mm in diameter to decrease glares and halos at night for patients with large pupils. This is accomplished without the significant increase in the amount of corneal tissues being removed and without significant increase in the time of treatment. There are currently two FDA approved excimer laser systems in the U.S. market with active eye trackers; the Visx Star S3 ActiveTrak™ has shorter treatment time. This short treatment time will avoid prolonged exposure of the cornea to air, hence, decreasing the chance of dehydration of the tissue that could lead to an irregular result affecting visual outcomes.

The Visx Star S3 ActiveTrak™ also has passive eye tracking limitations. These are eye movement limitations under which where the laser will not fire. The importance of these limitations is to keep the beam profile in optimum condition. As described by Marc G. Odrich, M.D. assistant professor of ophthalmology at Columbia University, New York City, and Medical Director for Visx Inc., as the eye rotates, the beam profile is compromised. "For example, hold a flashlight to the floor, " Odrich said. "There will be a circle of light on the floor. As you tilt the flashlight, the circle changes to an elliptical spot. The same will happen with the laser if fired at an oblique angle. As the angle increases, the profile changes from a circle to an ellipse."

There have been over 2 million laser surgical procedures performed with the Visx laser all over the world. Visx technology has proven track records of excellent visual outcomes. The addition of the eye tracker and variable spot scanning (VSS) added another degree of safety to help patients achieving excellent visual outcomes.